Rotatable furnace



` @CL 20,1931.,- R. c. BENNER m- AL Lazzs ROTATABLE FURNAGE Filed Dec. '7. 1928 3 SheatsmSheet l INVENTORS RAYMOND C. BENNR BY QEORCAE J. EASTER,

cLAREN E. wma, @Imac HAWKE ATTO NEY @CL 20, 1931. R. c. BENNER ET AL ROTATABLE FURNACE Filed Dec. 7, 1928 5 Sheets-Sheet 2 INVENTORS' RAYMQND @Bamm BY Gamesa J. EASTER.

QLAREN vm MMM C, ,m GE E H E ATTOR EY OC- 20, 1931- R. c. BENNER ETL 3,8279333 ROTATABLE FURNACE Filed DeC. '7. 1928 3 Sheets-Sheet 5 (il f lll Mk il lh "'Ii ATTOR N FY Patented Oct. 20, 1931 Unirse slr-Arie s" PATENT' OFFICE RAYMOND C. BEN'NER AND GEORGE J. EASTER, OF NIAGARA FALLS, NEW YORK, AND

CLARENCE E; HAWKE, 0F METUCHEN, NEW JERSEY, ASSIGNOR-S TO THE CARBORUN- DUM COMPANYL-OF NIAGARA FALLS, NEW YORK,A A CORPORATION OF PENNSYL- VANIA.

ROTATABLE FURNACE Application Med' December 7, 1328.' Serial' No.' 324,417.

This invention' relatesr-tot-furnaces :contain-- ingsilicon carbide' heating elements'-A in: which' the/furnace' isrevoifvedfor'oscillaztedl in: order'to stir 'upthe' chai-gel and subject it to quicker' and; more. uniform heating. Our principal 'ohjectsfteprovi de a rotatable fur'- naee-(which maybe continuouslyrotatedduring active opera/tion' or' oscillatedvbaclrv and forth; having readily." replaceableri-gid re sisters'whichv may housed-rat temperatures up -metallic resistors are used; since there isa tendency" tov. arcing: at the junctions-- between metal-1 andnon'fmetaeh this tendency' increase ing as the temperature ot' the Junction 111- creases. Still anotherifobjeetiishto show the 'adaptability of our improved'furnaice' to heattreatments-ofi materials inf gases other than" air-orat pressures:other than: atmospheric.'

Rotating urnaoes-of the 'electric are'type are' known; In! such.' furnaces 'thefheating islde'n veloped'- in Very restricted region! namely' atthe incandescentcores ofthe carbon' arcs; The use fof srllcon carbide resistor' rods rend'- orsY possible much more fumform heat1n': and

greater' energy: output; lVhilein' the case otthe electrica-rc heatersfthefveryhigh local temperatures; malte itl necessary' to 'have' the arc' approximately atthe center' of: the furnace` sil-icon carbide resistor rodsimay be distribntedxin groups '-aroundztheaoiis of the' fur'- naceormay'be mounted-'inithe refraotory'lining itself. Such' resistorsA in an' enclosed compartimenti maintain a= substantiallyuniform temperature over'about 80% of their length'. The latter method' of mounting would beimpraicticable' in' the' case ofthe elect-ric arc.' Zhen used' in'the refractory lining the silicon carbide resistor elements are easily protected-'trom'oxidation and. do not require replacement sooften'V as electric arc carbonsi This is? important' from the pointA ot 'ri'ew- -o continuity: of. 'service'.

Our'ixnproved rot-ating furnace' is illustrated. infthe accompanying drawings` in.

W hi ch- Fig-ure l isan elevation partly: 1n: section ot'afrotatable-f furnace'provided with stationary resistor elements; the' section being taken parallel tothe resistor rods;

F igllre' L A: is al'view similar to'4 that. ofi' Fig. lot'4 auer-lowered furnace inw-hielt the heating elements turn with th'e inutile;

Figure l-B -is a detail indicating a moans of' water-cooling the met-al terminalsotl the resistor rods shown in Fig. l;

Figure 2- relates to' the same type ot tur nace as in Fig. l. and indicates a sectional elevation ofth'e furnace taken at rightangles to Fig l on-vline'IL-H; i I

Figure 3; is afvertical section' ot' a rocking or osci'll'ating'furnace taken parallel to the resistor-rods;

Figure bis a section taken ati right angles toFig. italnenf on th'e'line lV*lV-;

Figure 5 is a section of' a rotatable cylindrical mulle in which the resistor rods ar(- separated from the' inuilierhy a reduced por'- tion of thelining-ot' tho inutile; the section being taken a=t= right angles to the :iti-s of rotation;

Figurel (3' isv a View ot the resistor rods of thelast-mentioned furnace shown in position in' grooves` in therefrac'tory lining with the cover which supports thel rods cut away;

Figure Z is a sectional View ot' the'uunil'o inthe last-mentioned type ot' furnace taken through theraxis of rotation;

Figure 84 is aview similar to Fig; (3 hut showing the-cover which is-just outside the resistor rods and which supports them;

Figure 9 isa detail View indicating a: manner otl mountingfa resistor'rofl' in the typo ot' furnace illustrated in l `igures 5-11.

Figure' 'l0-is a modili'cation'ot the mounting for a resistor rod shown in Fig. E); and

Figure. ll. imlicatesa; method ot watercooling the' metal terminals for thev resistor' rods in the type of furnace-shown in Figures- Vcate in-a conventional manner removable 4, at either end of the furnace. At the left end as shown in Fig. 1 the terminals 4 are supported on the rigid members 5. At the right hand end the water-cooled terminals 4 are subjected to adjustable spring pressure and are connected to and vsupported on spring-pressed rods which can slide through the rigid support 7. The springs 8 take care of the change of length of the silicon carbide rods 1 due to changes of temperature.

The muile in the type shown in Fig. 1 has a refractory lining 9 contained in an iron shell 10. The latter carries annular projections or tracks by means ofwhich the furnace may turn on rollers 11.` These supports 5 and 7 mayb'e inountedon a frame' so that the axis of-the furnace A fmay .be-horizontal or vision for water-cooling. The metal terminal 29 may be made of a high heat resisting alloy, for example of chrome iron containing about 27 percent chromium. The part 30 may be of iron welded on to 29. Water cireulation is indicated as taking place through 30, which has rubber hose connections at inlet and outlet. Electrical connections may be made at 31 orany convenient portion of the metal terminal. '1 y A plug is shown as at 33 in Fig. 2 to indimeans for closing an opening through which the chargemay be inserted or abstracted.

Figure 1-A indicates a type of rotatable furnace' which. may be. completely enclosed, 'the current being led in by means of stationpressed metal terminals are rotatable as a body with respect to the stationary brushes 27. Gas ports 42 and 43 respectively, may be provided for giving a non-oxidizing or other fornr of atmosphere in the Inutile as required. A certain amount of water-cooling may be effected by directing jets of water on the metal disks 5.

In Figures 3 and 4 there is shown a type of furnace adapted for an oscillating movement as contrasted with the type shown in Figures 1, l-A and 2, which are adapted for continuous rotation in one or the other direction. A removable plug 34 is shown for closing the outlet for the nished product. A somewhat larger charging opening is provided which may be closed by the plug 35. The resistor bars are mounted in a removable cover 13. Metal terminals 4 are indicated. These may be water-cooled as indicated in Fig. l-B.

Arods l are shown as mounted between chrome steel springs. The latter are fastened to 1n- S0 sulating blocks 36 by means of bolts 38 which are also connected to flexible leads 39 for `making electrical connection .with the rings 2l. The rings 214 are mounted on other insulating members 37. The latter Imay be bonded by means of refractory cement to the refractory lining of the inutile or otherwise fastened thereto. The cover 16 may be bound to the refractory by locking means not shown during the operating of the furnace. \Vhen unlocked the cover may be removed on disconnecting the electric leads.

In the modification shown in Fig. 10 the rigid bars 22 take the place of the springs 19. rIhe spring 40 takes care of changes of `length of the resistor rod dueto changes of temperature. The terminal 24 has a sliding contact with bar22.

In Fig. 11 means are shown by which metal terminals for non-metallic resistor elements may be water-cooled. The spring pressed metal terminals 41 are in thermal contact with troughs 26 which extend completely around the muiile, but these terminals should preferably be thermally insulated from the heat conducting inner lining 15 of the furnace. lVater -is dropped from pipes 25 through perforations 5l and is received after it has abstracted a certain amount of heat from the metal terminals in outlets 52.

N ichrome or similar metallic resistors are not suitable for use in heating furnaces above 11000 C. Resistor' rods of the type illustrated in our drawings but made of graphite or bonded carbonmay also be used at such low temperatures, where their tendency to oxidation is not too severe, but for use at temperatures above 1100o C. we may use silicon carbide resistors. The latter can be used at temperatures up to 1400o C. and when protected from oxidation can be used at temperatures up to 1600.o C.

From the foregoing description it will be seen that silicon carbide resistor rods may be used in a variety of rotating furnaces.

As compa-red with arc furnaces of this type they have the advantage of greater uniformity of heating and of longer life. Means for protecting the ends of the rods from arcing have been indicated in the drawing and in 130 the foregoing specification. The tendency to arcing is reduced by using metal terminals vwhich have low vapor pressures at the temperatures used. The temperatures at the contacts between metal and non-metal are in general kept down by water-cooling. The main parts or bodies of the resistor rods may be protected from oxidation by painting the rods with a non-reactive glaze such as is described in copending application No. 228,492, tiled Oct. 24, 1927. With these various precautions the life of the resistor rods will lbe much greater than that of the rods used in rotating arc furnaces.

As compared with metals silicon carbide has several advantages. On account of its higher resistivity (which is also higher than that of carbon) it can be used in rods of large cross-sectional area and shorter length than is possible in the case of metals and carbon resistors. Silicon carbide can be used up to temperatures of about-2000 C. It decomposes at 2200o C. It can be used therefore at temperatures much higher than metal resistors in commercial use. Silicon carbide has also a very high emissivity and a low coefficient of expansion. The furnace described in this specification may be used with a high input of energy because of the fact that silicon carbide does not melt below about 22000 C., at which temperature it decomposes, and also because it has a high emissivity and a high thermal conductivity.

Silicon carbide resistor rods have been used for five hundred hours in an enclosed mule. The length of time that they can be used depends on the temperature at which they are run, and on the means talen for protecting them from oxidation. Vith suitable precautions they may be used more than 100 hours at temperatures above 1100G C.

Ve claim:

l. In a rotatable furnace, non-metallic heating elements of a rigid self-supporting character mounted to rotate with aheating chamber and supported on a removable portion thereof, said heating elements being freely accessible for replacement when said portion of the heating chamber is removed.

2. In a rotatable electric furnace, non-metallic resistor eleme-nts mounted for rotation with said furnace, each of said elements being in butt-end engagement with a resilient metallic connecting terminal, Water-cooled metallic terminals for the same, and a removable portion of the furnace to which said resistor elements are ordinarily attached, the elements being freely accessible for replacement when said portion of the furnace is removed.

3. In an electric furnace an enclosed heating chamber mounted for rotation, and a plurality of rigid non-metallic resistors capable of withstanding temperatures greater than 1,100o C., each of said resistors having a buttend engagement with a metallic connecting terminal supported by said heating chamber, and said heating chamber having an inner surface which is curved in planes perpendicular to its axis of rotation whereby rotary displacements of the heating chamber change the position of the charge within the chamber with respect to the resistors.

4. A rotatable electric furnace having a compartment for material to be heated, a heat conducting lining adjacent said compartment and rigid non-metallic heating resistors mounted on a removable portion of said furnace in such a manner as to be freely accessible for replacement when said portion of the furnace is removed, said resistors being separated from the said compartment by the heat conducting lining.

5. In an electrical furnace, a refractory casing, non-metallic resistors within said casing for heating said furnace, each of said resistors being mounted for rotation with the furnace by butt-end engagement with at least one resilient metallic connecting terminal and a cover removable from said casing to which cover said resistors are removably attached.

6. In a rotatable furnace, a refractory casing, non-metallic resistors for heating said furnace, and a cover removable from said casing in which said resistors are mounted in such a manner as to be freely accessible for replacement when said cover is removed from the furnace.

7. In a rotatable electric furnace, a refractory casing, resistors consisting mainly of silicon carbide for heating said furnace, and a cover removable from said casing in which cover said resistors are mounted in such a manner as to be freely accessible for replacement when said cover is removed.

8. In an electrical furnace, a substantially air tight casing, non-metallic resistors for heating said furnace, and a cover removable from said casing, each of said resistors being mounted in butt-end engagement with short resilient metallic connectors attached to said cover.

RAYMOND C. BENNER. GEORGE J. EASTER. CLARENCE E. I-IA'WKE. 

